In lieu of all the technicalities and details, I'll hit ya with the bottom line.
For 7 star Thrawn you need:
Level 85, gear 8, all abilities omega'd (none zeta'd), and mods that focus on PROTECTION!! I can't stress that last detail enough for you. I too tried the Thrawn event a long while ago multiple times with higher speed Phoenix toons and lost due to not enough protection to absorb the hit of Thrawns Fracture ability. While speed is somewhat important for this event, it's not the most important thing... PROTECTION is. Try getting the mods with a 23.5% protection primary stat. Due that several times and you'll fly by the event with ease. Take a look if you want at my Phoenix toons. (I've done literally nothing to them after defeating the event months ago.) Notice that I didn't use Sabine either. ;) Good luck and MTFBWY! :smiley: Feel free to pm me if ya want. :) Joe